This invention pertains to rotary airlocks. More specifically, the present invention relates to rotary airlocks that are used for feeding a metered amount of material under pressure or vacuum while sealing in air and the material.
Conventional airlocks include a cylindrical housing, a shaft extending therethrough, and a plurality of vanes which are secured to the shaft. The vanes have three working edges which desirably have a minimum clearance relative to the housing, or a blade may be secured to the vane and extend outwardly therefrom to provide a minimum clearance relative to the housing. An inlet and outlet communicate with a chamber defined by the housing.
The airlocks are frequently used to feed a metered amount of material from a top bin into the airlock inlet and out of the airlock outlet to a bottom bin or discharge line. Since airlocks are normally used with a pressure or partial vacuum in the discharge line, it is important to maintain the smallest possible clearance between the vanes (or blades) and the housing to minimize the leakage of air and material to thereby maximize the efficiency of the airlock.
There is always some air leakage. Some clearance must be provided between the vanes and the housing to allow for rotation of the shaft and vanes. In addition, as the airlock is used, the amount of leadage of air and material increases due to wear of the housing and the working edges of the vanes or blades which increases the size of the gap therebetween. Furthermore, the pockets which are defined between the shaft, housing and adjacent vanes, cause some leakage when they return to the airlock inlet.
In an attempt to solve the problem of wear, some prior art devices disclose blades that can be replaced in their entirety as wear occurs. The disadvantages of this arrangement are the cost of the new blades and the cost of the down time when the airlock is removed from service to effect repair.
Other prior art devices disclose tips which are secured to the vanes and are adjustable radially relative to the shaft. Inasmuch as only a single tip is attached to each vane and the tip is movable only radially, no adjustment can be made to compensate for the wear of the tips along the ends of the housing.
Consquently, the prior art devices fail to solve the problem of minimizing the clearance between the vanes (or blades) and the housing to reduce leakage of air and material after wear occurs during use of the airlock.